The present invention relates to an analog-to-digital (A/D) converter which eliminates the need for accurate components but provides high conversion accuracy even when an analog signal input thereto is at a low level.
FIG. 1 schematically illustrates A/D conversion processing which has been conventionally performed in a variety of applications. An input analog signal is converted to a digital signal by an A/D converter having a resolution of N bits. In this event, the accuracy of the A/D conversion is determined by the number of bits N of the used A/D converter.
With the illustrated configuration, however, since only one A/D converter is used, the dynamic range is determined by the accuracy of the A/D converter. Therefore, a sufficient dynamic range cannot be ensured if an A/D converter with a low accuracy is used. On the contrary, when an accurate A/D converter is employed for ensuring a sufficient dynamic range, the cost of the entire apparatus is increased due to a high cost of the A/D converter itself.
In addition, in the A/D conversion processing illustrated in FIG. 1, noise produced by the A/D converter itself is often larger than quantization noise which is determined by the resolution of N bits. The noise produced by the A/D converter itself causes a higher noise floor, thereby degrading the dynamic range in consequence.